Our asthma research program involves both exposure assessment and prevention components, and focuses on the relationship between exposure to common indoor allergens and asthma prevalence/morbidity. The National Allergen Survey, a study of allergen types and levels in floor and bedding dust in the nation's housing, is the first study to provide estimates of allergen exposure in the U.S. population. It encompasses 831 homes in 75 primary sampling units located throughout the country. The major endpoints are measurements of dust mite, cockroach, cat, dog, mouse, rat and fungal allergen levels, and endotoxin in dust samples collected from an array of sites in the surveyed homes. Results from analysis of dust mite allergens suggest that approximately 24% of U.S. homes have beds that contain >10 microgram dust mite allergen/gram dust (a level previously associated with symptomatic asthma) and approximately 46% of U.S. homes have beds that contain >2 microgram dust mite allergen/gram dust (a level previously associated with mite allergen sensitization). The likelihood of having a high dust mite allergen level in the bed was greater for older homes, non-western region homes, lower income households and bedrooms with higher humidity. Dog and cat allergens were universally present in U.S. homes. Levels were higher among homes with an indoor dog and/or cat; however, among homes without an indoor pet, mean allergen concentrations were still well above proposed thresholds for allergic sensitization and disease. Mouse allergen was detectable in approximately 82% of U.S. homes and levels exceeded proposed sentization thresholds in 22% of homes. The likelihood of having high mouse allergen levels in the kitchen was greater in high rise apartments, mobile homes, older homes, low income homes, homes where rodent or cockroach problems were reported, and when floor mopping was performed instead of vacuuming. Alternaria allergen was present in 95-99% of U.S. homes. Multivariable linear regression analysis showed that age of home, geographic region, urbanization, poverty, race, observed mold and moisture problems, use of a dehumidifier and presence of pets were independent predictors of Alternaria concentrations. This nationally representative survey has (a) provided current estimates of indoor allergen exposure in the U.S. population, (b) established a database that can be used to stimulate future studies which attempt to correlate allergen exposure to disease outcome, (c) provided a baseline that can be used as a reference point for future allergen surveys, and (d) facilitated evaluation of regional, ethnic, socioeconomic, and housing characteristic differences in the allergen burden. We have also conducted a randomized clinical trial to test the feasibility/effectiveness of environmental interventions in reducing cockroach allergen levels in inner-city North Carolina homes. Our study demonstrated that the combination of cockroach extermination and intensive cleaning can significantly reduce cockroach allergen levels in highly infested homes. Moreover, the effect can be maintained for up to 12 months with continued extermination. Cockroach extermination alone was also found to significantly reduce cockroach allergen levels in low income homes over a 12 month period. The results of these studies will be used to design a secondary prevention trial to determine if environmental intervention aimed at reducing indoor allergen levels can decrease the morbidity of asthma in high risk children living in poverty.